For years now, we’ve assumed that sixty-some million years ago, a comet or asteroid crashed to earth, landing near what is now the Yucatan, creating a huge earthquake kicking up enough an enormous amount of debris, and wiping out the dinosaurs and other large creatures. Lisa Randall, a Harvard cosmologist, speculates that the comet did not act alone: That a disc of dark matter at the heart of the galaxy knocked the comet out of orbit and sent it on its path toward the earth. The solar system’s orbit through the Milky Way allowed this disc to trigger comet strikes every 30-35 million years — which coincides with periodic waves of extinctions on earth.
But what is dark matter and why does it have anything to do with us? Randall explains how this might have worked — complete with charts — in “Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe.”
“A good theory is an act of the informed imagination — it reaches toward the unknown while grounded in the firmest foundations of the known,” Maria Popova wrote of Randall’s book in The New York Times Sunday Book Review. “If correct, Randall’s theory would require us to radically reappraise some of our most fundamental assumptions about the universe and our own existence.”
We spoke to Randall from New York City. The interview has been lightly edited for clarity.
So you were concerned with the density of dark matter, and gave a lecture about your research. How did you end up dealing with the dinosaurs?
I was giving a talk in Arizona, and [physicist] Paul Davies said, “So is this what was responsible for the extinction of the dinosaurs?” Or something of that nature. I had no idea what he was talking about. But then he told me about the weak evidence for periodicity that’s in the crater record.
What it really boiled down to is — is there something in our galactic environment that could trigger periodic meteor strikes? There’s some marginal evidence that large-impact craters occur on a periodic basis — between 30 and 35 million years. Small stuff hits all the time. But the question is whether, with large stuff, there’s something predictive there — that it’s not just random. The suggestion for this is the Oort Cloud. Thousands of times farther away than Earth is from the sun, is a bunch of icy bodies that are very weakly bound … They are so far from the sun that its gravitational force keeps them in a weakly-bound orbit. And they turn into long-period comets. Sometimes their paths get so distorted that they enter the inner solar system.
And sometimes, if you have some kick, it might go out of the orbit altogether. So the question becomes, “What could trigger comet strikes — the dislodging of objects — on a periodic basis?”
Other people had tried to answer this question. But nothing on the ordinary matter sector seemed to work. But if there is this dark disc, as the solar system goes around the Milky Way, it also bobs up and down, along the galactic plane … How often it does that has to do with what’s in the galactic plane, because that’s the force that makes [the solar system] go up and down. Without dark matter, it would do it every 55 or 60 million years — much too slowly. But if there is dark matter, it would happen much more quickly … The idea is that [the solar system] goes through this dark disc, and that would trigger comet strikes.
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